Controlled atmosphere stunning of chicken, turkeys, and other poultry is a process used at the incoming or intake end of a poultry processing plant, in which a breathable non-oxygen gas is substituted for at least a portion of the atmospheric air that is initially in and around the cage or containment area for the poultry, to thereby deplete that local atmosphere of oxygen. Commonly used non-oxygen gases include nitrogen and carbon dioxide, both of which are found in atmospheric air. For animal welfare and meat quality purposes, it is desirable for the poultry or livestock to breathe the oxygen-depleted atmosphere without becoming alarmed or attempting to escape their confines, which can result in unintended harm to the animals and reduced meat quality due to bruising and broken legs or wings. From a plant production efficiency standpoint, it is preferred for the stunning process to take place as quickly and humanely as possible, while minimizing the wasting of breathable non-oxygen gas.